gence of opinion induced us to attempt to solve the problem by a To

ON

THE

RESPIRATORY

FUNCTION

OF

THE

INTER-

NAL

INTERCOSTAL

MUSCLES.

By

H.

NEWETL

MARTIN,

Professor

of

Biology

in

the

Johns

Hopkins

University,

Baltimore,

U.

S.

A.,

and

EDWARD

MUSSEY

HARTWELL,

M.A.

Plate

I.

AN

inspection

of

the

ordinary

text-books

of

Physiology

is

sufficient

to

shew

that

the

part

played

by

the

internal

intercostal

muscles,

in

the

production

of

the

respiratory

movements

of

the

mamimal,

is

still

a

subject

upon

which

there

is

no

agreement

among

Physiologists.

Thus

in

the

text-books

accessible

to

us

we

find

these

muscles,

in

some

cases

with

more

or

less

reserve,

described

as

inspiratory

in

function

(Dalton,

Ludwig,

Vierordt);

or

as

both

inspiratory

and

expiratory

in

different

portions

(Carpenter,

Flint,

Hermann,

Mc

Kendrick);

or

as

expiratory

only

(Donders,

Funke);

while

Foster

says

that

their

action

must

at

present

be

left

an

open

question.

This

diver-

gence

of

opinion

induced

us

to

attempt

to

solve

the

problem

by

a

method

which,

so

far

as

we

know,

has

not

hitherto

been

employed.

To

arrive

at

a

decision

as to

the

function

of

these

muscles

as

rib

elevators

or

rib

depressors,

from

a

simple

mechanical

study

of

their

attachments

seems

impracticable;

on

account

of

the

irregular

shape

of

the

ribs

and

the

doubt

which

must

exist

as

to

whether

the

upper

or

the

lower

rib,

to

which

one

of

these

muscles

is

fixed,

is

to

be

regarded

as

its

origin

or

insertion.

Moreover,

if

experiments

be

made

in

which

any

or

all

of

the

other

muscles

be

cut

away,

then

direct

observation

of

the

movement

of

the

ribs

which

follows

when

the

in-

ternal

intercostals

contract

is

useless

so

far

as

settling

their

function

goes;

because

we

do

not

know

that

we

have

not

removed

some

inuscles

which,

in

ordinary

breathing,

held

fast

either

the

upper

or

lower

rib

and

so

determined

either

the

inspiratory

(rib

elevating)

or

the

ex-

piratory

(rib

depressing)

function

of

the

muscle.

The

observation

of

the

result

of

direct

electrical

stimulation

of

these

muscles

is

also

not

de-

cisive:

unless

all

the

other

muscles

which

work

with

them

in

breathing,

be

also

excited

in

proper

order

and

degree;

which

is

impossible.

Un-

less

this

be

done,

however,

we

cannot

by

this

means

tell

which

rib

is

normally

the

fixed

one,

when

one

of

these

muscles

contracts.

It

FUNCTION

OF

IVTERNAL

INTERCOSTAL

MUSCLES.

25

seemed

to

us,

however,

that,

by

isolating

an

internal

intercostal

and

then

observing

whether

it

contracted

simultaneously

or

alternately

with

the

diaphragm,

its

function

could

be

settled;

since,

from

the

general

co-ordination

of

muscular

contractions

in

the

respiratory

movements,

there

can

be

no

doubt

that

muscles

excited

from

the

respiratory

centre

and

contracting

during

respiration

simultaneously

with

the

diaphragm,

are

inspiratory

muscles;

and

that

those

contracting

when

it

relaxes,

are

expiratory.

Dogs

and

cats

were

employed

in

our

experiments.

The

animals

having

been

etherized,

tracheotomy

was

performed

and

the

apparatus

for

artificial

respiration

connected

with

the

wind-pipe.

The

abdomen

was

opened

by

an

incision

along

the

linea

alba

and

a

transverse

in-

cision,

so

as

to

expose

the

diaphragm

from

below.

The

skin

and

the

serratus

and

pectoral

and

other

muscles

were

then

dissected

away

from

one

side

of

the

chest

so

as

to

lay

bare

the

external

intercostal

muscles

from

the

fourth

or

fifth

to

the

ninth

or

tenth

ribs:

except

where

they

were

covered

at

their

dorsal

portions

by

the

muscles

running

alongside

of

the

vertebral

column.

During

this

operation

several

small

vessels

commonly

required

tying,

especially

in

the

dog.

One

intercostal

space,

say

that

between

the

eighth

and

ninth

ribs,

was

then

selected

and

the

anterior

part

of

the

external

intercostal

muscle

divided,

near

its

attachment

to

the

lower

of

the

two

ribs,

for

from

an

inch

to

an

inch

and

a

half

at

its

sternal

end.

The

internal

intercostal,

which

was

carefully

avoided

during

the

operation,

then

remained

alone,

with

the

pleura

uniting

the

front

parts

of

the

two

ribs.

The

eighth

and

ninth

costal

cartilages

and

the

tissues

between

them

were

next

divided,

the

chest

opened

and

the

artificial

respiration

apparatus

set

at

work.

The

tissues

in

the

seventh

and

ninth

inter-

costal

spaces

were

then

completely

divided

nearly

all

the

way

back

to

the

vertebral

column.

Next,

from

the

pleural

side,

a

fine-bladed

knife

was

inserted

be-

tween

the

eighth

intercostal

nerve

and

the

eighth

rib

near

the

verte-

bral

column

and

an

incision

carried

forwards,

without

cutting

the

nerve,

until

it

reached

the

outer

end

of

the

region

where

the

external

intercostal

muscle

had

been

divided.

In

making

this

incision

we

have

found

it

impossible

to

avoid

cutting

the

intercostal

vein

of

the

space

operated

upon;

the

artery

was

sometimes

divided

also,

but

this

did

not

seriously

impair

the

result.

An

incision

of

similar

extent

was

then

made

along

the

upper

border

of

the

ninth

rib,

and

finally

a

bit

of

both

ribs

corresponding

in

extent

and

position

to

these

incisions

w

26

H.

NEWELL

MARTIN

AND

E.

31.

IHARTWELL.

completely

cut

away

by

bone

forceps.

By

this

means

we

obtained

from

an

inch

to

an

inch

and

a

half

of

the

sternal

ends

of

the

eighth

an(I

ninth

ribs,

united

only

by

the

internal

intercostal

muscle

and

the

pleura,

and

connected

with

the

rest

of

the

body

by

a

band

of

tissues

consisting

of

the

intercostal

nerve

(and

artery)

and

some

muscle

and

pleura.

The

remaining

sternal

piece

of

one

of

the

ribs,

sometimes

the

upper,

sometimes

the

lower,

was

then

fixed

in

a

clamp

and

placed

in

such

a

position

that

the

band

of

tissues

above

referred

to

hung

quite

lax;

so

that

movements

of

the

ribs

or

even

of

the

whole

trunk,

unless

unusually

powerful,

could

not,

through

it,

drag

on

the

piece

of

muscle

to

be

experimented

upon.

A

string

was

then

attached

to

the

other

rib

and

passed

over

a

pulley

to

a

lever

which

carried

a

weight

and

extended

the

muscle.

This

lever

carried

a

pen

which

wrote

on

the

paper

of

a

Ludwig's

Kymographion.

A

tambour

was

fixed

beneath

the

diaphragm

and

connected

with

another.

This

latter

tambour

was

provided

with

a

lever

which

recorded

the

contractions

of

the

diaphragm

immediately

under

the

lever

connected

with

the

intercostal

muscle.

The

artificial

respiration

was

then

stopped,

and

the

animal

was

generally

found

apnceic.

The

further

course

of

events

differ

in

the

dog,

and

cat.

In

the

former

the

diaphragm,

when

the

apncea

passed

off,

made

a

few

contractions

without

any

activity

of

the

intercostal

muscle:

but

this

latter

soon

began

to

contract

in

regular

alternation

with

the

diaphragm

and

before

the

occurrence

of

expiratory

convulsions;

in

fact

with

the

commencement

of

dyspncea.

Having

made

a

few

con-

tractions,

varying

in

number

from

fifteen

to

five

or

six,

it

again

ceased

its

activity,

although

the

animal

became

more

and

more

dyspnceic

as

evinced

by

the

contractions

of

the

diaphragm.

This

cessation

seems

due

to

the exhaustion

of

the

muscle

occurring

rapidly

from

exposure

and

the

interference

with

its

blood

supply;

since

the

contractions

become

successively

feebler

before

disappearing;

and

if

artificial

respi-

ration

be

resumed

and

the

animal

kept

alive

until

the

muscle

has

had

a

period

of

rest,

then

on

again

stopping

the

respiration

the

phenomena

are

repeated,

but

the

muscle

makes

a

smaller

number

of

contractions.

We

have

seen

this

restoration

occur

five

times

in

the

same

dog.

The

Figure,

P1.

I.

to

be

read

from

right

to

left,

shews

the

tracing

of

the

fourth

set

of

contractions

obtained

in

one

experiment

with

the

sixth

internal

intercostal

muscle

of

a

dog;

the

ascents

of

the

upper

line

indicate

con-

tractions

of

the

intercostal

muscle;

and

those

of

the

lower

line

contrac-

tions

of

the

diaphragm.

It

will

be

seen

that

they

alternate

perfectly.

FUNCTION

OF

INTERNAL

INTERCOSTAL

MUSCLES.

27

In

order

to

get

accurate

tracings,

we

have

found

it

necessary

to

divide

completely

the

straight

and

oblique

muscles

of

the

abdomen:

otherwise

the

action

of

these

in

dyspncea,

as

expiratory

muscles,

when

pulling

down

the

ribs

is

apt

to

compress

the

abdomen

and

falsify

the

record

of

the

tambour

beneath

the

diaphragm.

In

order

to

see

the

phenomenon,

however,

it is

not

necessary

to

have

any

recording

apparatus

at

all:

the

alternating

contractions

of

the

diaphragm

and

the

intercostal

muscle

can

be

readily

observed

directly:

and

the

latter

occur

in

greater

vigour

no

doubt

from

the

absence

of

the

shock

due

to

the

extensive

abdominal

incisions

and

the

exposure

of

the

viscera.

In

the

cat

the

internal

intercostal

muscle

rarely

contracts

until

the

occurrence

of

expiratory

convulsions;

but

during

these

it

contracts

very

powerfully

when

the

diaphragm

is

most

completely

relaxed.

While

the

convulsions

occur,

it is

necessary

to

hold

the

vertebral

column

of

the

animal

very

firmly

in

order

to

prevent

any

drag

on

the

intercostal

nerve.

Usually

the

muscle

is

exhausted

during

these

contractions;

but

on

these

convulsions

passing

off

we

have

sometimes

seen

it

in

action

alternately

with

the

first

few

of

the

slow

final

contractions

of

the

diaphragm;

its

contraction

occurring

immediately

after

the

diaphragmatic,

and

beino

followed

by

a

shorter

or

longer

pause

before

the

next

diaphragmatic

contraction

began.

In

some

experiments

the

strip

of

muscle

used

was

the

portion

between

the,

costal

cartilages;

which

is

not

covered

by

the

external

intercostal.

The

results

thus

obtained

were

the

same

as

when

a

por-

tion

lyina

between

the

bony

ribs

was

employed.

The

results

of

our

experiments,

we

believe,

shew

decisively

that

the

internal

intercostal

muscles

are

expiratory

in

function

throughout

their

whole

extent;

at

least

in

the

dog

and

cat:

and

that

in

the

former

animal

they

are

almost

"

ordinary"

muscles

of

respiration,

coming

into

play

very

early

in

dyspncea,

while

in

the

latter

they

are

"

extraordinary

"

respiratory

muscles,

only

active

during

extreme

dyspncea;

unless

the

later

action

be

ascribed

to

a

diminution

of

the

irritability

of

the

muscle,

brought

about

by

the

unnatural

conditions

to

which

it

was

exposed,

which

may,

perhaps,

influence

more

quickly

the

thinner

muscles

of

the

cat

than

the

thicker

ones

of

the

dog.

Jolzrn/.

RhkyiahyZgy7;

Vol.

J11

-Pb

F

Huthl,

LithY

Edani