Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/1109/
THYMUS GLAND. 
1099 
cess we here find occurring the superaddition 
of a thymus gland, — its first appearance in 
the ascending scale of organization.” Among 
the Perennibranchiata it is very interesting to 
observe, that the gland is gradually suppressed 
in proportion as the respiration becomes more 
completely aquatic, a thymus is found in the 
Menopoma, Amphiuma, Axolotl, and Meno- 
branchus, but not in the Siren or Proteus ; its 
position is rather peculiar, it lies in the neck, 
on each side, along the lateral aspect of the 
spine, just behind that prolongation of mucous 
membrane which unites the branchial cavity 
to the pharynx. 
Pisces.—In fishes Mr. Simonhas been unable 
to discover any trace of a thymus, after search¬ 
ing, carefully, in more than twenty genera ; 
this result accords well with the absence of 
the gland in the fish-like batrachian larva, and 
with its disappearance in the lowest Perenni¬ 
branchiata. 
The following are the conclusions which 
the eminent physiologist, so often referred to, 
deduces from a survey of his detailed and 
elaborate investigation. (L) The presence 
of the thymus gland is co-extensive with pul¬ 
monary respiration. (2.) Its shape and po¬ 
sition are variable and unimportant. (3.) Its 
size and duration are, generally speaking, in 
proportion to the habitual or periodical inac¬ 
tivity of the animal. (4.) Where it remains 
as a persistent organ, it is usually but one of 
several means for the accumulation of nutri¬ 
tive material ; its continuance, under such 
circumstances is generally accompanied — 
though in some instances superseded —by a 
peculiar accessory contrivance, the fat body. 
Physiology. — The time is now past when 
an eminent physiologist could declare of the 
organs usually known as glands without ducts, 
“that in regard of their intimate structure and 
physiological meaning, they are all equally 
and utterly unknown to us.” With respect 
to their structure, it may, I think, be said, that 
they are as well understood, or perhaps even 
better than the true glands, being in fact less 
complex, and their constituent parts less in¬ 
dependent. Their physiological meaning, it 
must be confessed, is still obscure ; yet even on 
this dark part of the demesne of our science 
light is beginning to break, which we may fairly 
hope will continue to brighten. 
The results afforded by examination of the 
thymus in the lower animals seem certainly to 
connect the gland most closely with pulmo¬ 
nary organs of respiration, and it would, 
therefore, seem a natural conclusion, that it 
subserves some purpose which has to do with 
the aeration of the blood. It is also found 
that the size of the gland may vary in a short 
space of time very considerably, that is, that 
its contents are capable of being absorbed very 
quickly, as proved by the fact mentioned by 
Mr. Gulliver, that in over-driven lambs, the 
thymus will soon shrink remarkably, and be 
nearly drained of its contents, but will be¬ 
come as quickly distended again during rest 
and plentiful nourishment. This seems to 
imply that the material necessary for the 
supply of the respiratory process is furnished 
by the thymus, which thus, in Mr. Simon’s 
words “ fulfils its use as a sinking-fund in 
the service of respiration.” The persistence 
of the gland, moreover, is observed to vary 
considerably according to the muscular ac¬ 
tivity of the animal, thus it disappears quickly 
in young oxen put to the plough, it endures 
longer in animals of quiet habits than in the 
restless and energetic beasts of prey, and 
vanishes at a very early period in the class of 
birds, while it persists long in that of reptiles. 
From this it seems to follow, that the use 
fulfilled by the gland in the service of res¬ 
piration is more or less superseded when the 
muscular system is called into a high state of 
activity, i.e. when there is considerable waste 
of tissue yielding fuel for respiration. In 
the hibernating animal, where the gland, pre¬ 
parative to the winter sleep, is transformed 
into a mass of fat, its application to the de¬ 
mands of the respirtory process seems 
scarcely doubtful, as the chemical nature of 
the contents of its cavities is then peculiarly 
appropriate to neutaralise theoxydising agency 
of the air. 
Probable, however, as these views may ap¬ 
pear, they have been confronted by the fol¬ 
lowing weighty objections. An able physio¬ 
logist, in the Brit, and Foreign Med. Re¬ 
view, observes, that the condition of young, 
rapidly growing animals, and that of hiber¬ 
nating animals, are rather opposite than pa- 
rellel, that whereas in the latter, the waste of 
the tissues is reduced to a minimum, in the 
former it is certainly greater than in the adult, 
so that there can be no deficiency of effete 
material to feed the respiratory furnace. The 
demand in the young creature is for plastic 
materials, out of which the rapidly growing 
and rapidly changing structures may be built 
up and renewed. “ On the other hand, in the 
hibernating animals all the nutritive actions 
are at zero, and the respiration for a long 
period is entirely dependent on the stores of 
fatty matter which have previously been set 
apart from the food. The demand is here for 
combustible materials.” 
The writer then observes, that the che¬ 
mical nature of the contents of the thymus 
correspond so exactly at the two periods of 
active growth and hibernation to the kind of 
demand which must then exist in the system, 
that he conceives it more probable that the 
use of the gland at these times is different ; 
in the one slowly yielding up its hydro-car- 
bonous contents to supply fuel to the respi¬ 
ratory process, in the other performing the 
principal part in elaborating, by means of its 
myriad nuclei, fibrine from albumen, the plastic 
from the non-plastic element. “ As the de¬ 
mand for plastic material becomes less ener¬ 
getic the thymus diminishes in size and dis¬ 
appears, the production of plastic matter 
within the absorbent and sanguiferous vessels 
being then sufficient for the wants of the sys¬ 
tem. Or if the organ remains,” its struc¬ 
ture “ and the nature of its function changes,
        

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