Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Todd, Robert Bentley
groups of Birds that engage us, and that 
differ so essentially in their powers of engender¬ 
ing caloric. In the one and in the other we 
observe the same difference in the state of the 
general strength which we have observed in the 
corresponding groups of the Mammalia. In 
the one which cools rapidly, there is the same 
state of weakness, of general impotency ; in the 
other the young are in a condition to walk, and 
in a certain sense to shift for themselves as soon 
as they have escaped from the shell. 
We perceive then in the first place, that the 
nervous system is much less energetic in the 
former than in the latter group ; and in the 
second place, that the digestive powers are in an 
equal degree inferior in strength ; for they are 
not only unable to take food of themselves from 
muscular incapacity, but also from the lack of 
the requisite instinct, and, farther, from their 
digestive organs not being in a condition to 
elaborate food to any extent. It is on this last 
account that the parents supply their young 
with food which has suffered maceration in 
their own crops, or has even in their stomachs 
undergone a kind of incipient or partial solu¬ 
tion ; or otherwise the parents have the instinct 
to select such articles as are easiest of digestion, 
and best fitted for the weakly state of the 
digestive organs of their progeny. We have 
already observed that a defect in the powers of 
digestion implies a corresponding imperfection 
in the blood. Whence we must conclude by 
analogy that the blood in the birds of the first 
group is inferior in quality to that of the birds 
of the second group. We consequently still 
find the two general conditions which regulate 
the production of heat throughout the animal 
kingdom—the state of the blood, the state of 
the nervous system. 
The same principles are applicable to the 
first period in the existence of all animals, 
without distinction of groups, as compared with 
adults. On the one hand we have ascertained 
that all without exception have a temperature 
lower than that of their parents ; on the other, 
nothing can be more manifest than their inferi¬ 
ority with reference to the energy of the nervous 
system. And more attentive and extensive ex¬ 
amination shows that this extends in like man¬ 
ner to the digestive functions, and consequently 
to those of nutrition generally. 
Let us first turn our eyes to the Mammalia. 
All of these are evidently inferior in this respect 
to the adult. This is proclaimed in the distin¬ 
guishing character of the class : the females are 
provided with glands for the purpose of prepa¬ 
ring a food appropriate to the state of weakness 
of their young. The state of the mouth of the 
young is a sufficient index of the defective 
power of the digestive organs ; the jaws are 
either wholly or partially without teeth. The 
softness, delicacy, paleness of colour, and insi¬ 
pidity of the tissues of young Mammalia, com¬ 
plete the evidence of the imperfect elaboration 
of the nutrient juices. If, therefore, the first 
and last products of the nutritive functions are 
in an inferior condition, can we suppose that 
the intermediate product, the blood, will not 
participate in this inferiority? We have already 
shown in what this consists among the Birds of 
the first group. With regard to the second, the 
general considerations relative to the difference 
of the tissues is equally applicable to them, and 
these considerations possess a high value. 
When very young warm-blooded animals, with¬ 
out any exception, are compared in this respect 
to the cold-blooded Vertebrata, we perceive a 
great analogy in their component tissues, which 
are softer and less savoury than among the 
adults of warm-blooded animals. It is thus 
that we can account for a striking anomaly in 
the nervous system of young warm-blooded 
animals, especially Mammalia. Their nervous 
system, particularly the encephalon, bears a 
higher proportionate ratio to the whole body 
than it does in the adult ; but the softness and 
the other characters of the tissue of this organ 
in early life cause it to approximate in a re¬ 
markable manner in appearance and character 
to the same tissue in the cold-blooded Verte¬ 
brata. If, therefore, the relative volume predo¬ 
minate in early life, one of the conditions 
favourable to calorification, the inferiority in 
respect of tissue counterbalances this advan¬ 
tage, and is only compatible with very inferior 
manifestations of energy. 
It is obvious then that there is a universally 
pervading analogy between warm-blooded ani¬ 
mals in the first stages of their existence and 
adult cold-blooded Vertebrata, and that the pa¬ 
rallel holds good, not merely with reference to 
their inferior power of producing heat, but also 
with regard to the functions of nutrition gene¬ 
rally and the functions of the nervous system. 
There is one point upon which it is highly ne¬ 
cessary to insist, inasmuch as it is of the greatest 
importance, both theoretically and practically ; 
it is this : that the analogy in the direction in¬ 
dicated is by so much the more remarkable as 
the warm-blooded animal is born with charac¬ 
ters which distinguish it more strikingly from 
those it possesses when arrived at maturity. If 
it is born with the eyes closed, or without fur 
or feathers, instead of with the eyes open and 
the body covered with a fur coat or a thick 
down, it is because the creature comes into the 
world less perfectly developed in every respect, 
and the whole economy is more closely allied 
to that of inferior orders. This, in other words, 
is as much as to say that the creature is born 
at a period relatively precocious, or in a more 
imperfect condition. Whence it may be in¬ 
ferred that those warm-blooded animals which 
are born at a period short of the ordinary term 
of utero-gestation among the more perfect spe¬ 
cies, will present a more marked analogy with 
the cold-blooded tribes. Man himself will 
form no exception to this rule, which must be 
quite general. The verification of this law has 
been completed by the physiological experiments 
of the writer. A child born at the seventh 
month, perfectly healthy, and which had come 
into the world with so little difficulty that the 
accoucheur could not be fetched in time to re¬ 
ceive it, had been well clothed near a good fire 
when the temperature was taken at the axilla. 
This was found no higher than 32° c. (under 
90° F.). Now we have seen that the mean of


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