NUTRITION. 
difficulty of respiration. It is in the different 
forms of tubercular deposit that we see the 
gradation most strikingly displayed between the 
euplastic and the aplastic formations. In the 
semi-transparent, miliary, grey, and tough yel- 
low forms of tubercle, we find traces of organi- 
zation in the form of cells and fibres, more or 
less obvious ; these being sometimes almost as 
paeetly formed as those of plastic lymph, at 
* least on the superficial part of the deposit, 
which is in immediate relation with the living 
Structures around, and sometimes so degen- 
erated as scarcely to be distinguishable. In no 
instances do such deposits ever undergo further 
organization, and therefore they must be re- 
_ garded as caco-plastic. But in the opaque, 
_ ¢rude, or yellow tubercle, we do not find even 
these traces of definite structure; for the matter 
of which it consists is altogether granular, more 
resembling that which we find in an albuminous 
coagulum. The larger the proportion of this 
kind of matter in a tubercular deposit, the more 
is it prone to soften, whilst the semi-organized 
tubercle has more tendency to contraction. 
Microscopic appearances of tubercular matter in the 
lungs, after Gulliver. 
_ To the left, magnified 190 diameters, is shown a 
‘central portion of tubercle, from the lungs of a man 
ged 22, who died of pulmonary consumption; the 
tubercle is contained in the air-cells, and surrounded 
by the fibres of their walls. To the right is depicted 
; ne of the same tubercle, separated and magnified 
about 820 diameters. 
4 Now although tubercular matter may be 
slowly and insidiously deposited, by a kind of 
degradation of the ordinary nutritive process, 
“yet it cannot be doubted that inflammation has 
great tendency to favour it; so that a larger 
uantity may be produced in the lungs, after a 
monia has existed for a day or two, than it 
uld have required years to generate in the 
ious mode. But the character of the de- 
it still remains the same ; and its relation to 
1 plastic element of the blood is shown by the 
interesting fact, of no unfrequent occurrence,— 
hat, in a pneumonia affecting a tuberculous 
subject, plastic lymph is thrown out in one part, 
hilst tubercular matter is deposited in another. 
Now inflammation, producing a rapid deposi- 
tion of tubercular matter, is peculiarly liable to 
arise in organs which have been previously 
* From Wagner’s Physiology, p. 360. 
755 
affected with chronic tubercular deposits, by an 
impairment of the process of textural nutrition ; 
for these deposits, acting like foreign bodies, 
may of themselves become sources of irritation ; 
sd, the perversion of seammnetice and func- 
tions of the part renders it peculiarly suscep- 
tible of the influence of external morbific 
causes. These views, at which several recent 
os hook ay and pathologists have arrived on 
independent grounds, seem to reconcile or 
supersede all the discordant opinions which 
have been upheld at different times regarding 
the nature of tubercle, and lead to the soundest 
views with respect to the treatment of the 
diathesis. 
Parasitic growths——Besides the products 
of disordered nutrition, which have been just 
considered, there is another class of morbid 
structures, differing from the preceding in well- 
marked and important characters. Their exist- 
ence and mode of growth cannot generally be 
traced to simple variations in the local circula- 
tion and in the formative powers of the parts 
affected ; and they enjoy an independent vitality, 
which causes their maintenance and increase to 
be influenced but little by the state of the 
textures around, except so far as this may 
affect the supply of blood which they receive. 
They bear a certain resemblance to other tis- 
sues, in an early stage of the developement of 
the latter; being for the most part composed of 
cells and fibres, combined in different modes’: 
and they also correspond with them in chemical 
constitution. It is by this last character, in- 
deed, that they are to be distinguished from the 
vegetable organisms, which are unquestionably 
developed occasionally in the living animal 
body, and which often closely resemble them 
in aspect. The best practical division of 
parasitic growths is into the non-malignant and: 
the malignant ;—the former being of local 
origin, not tending to reappear in distant parts 
of the body, and having no injurious effect 
upon the surrounding tissues, except by the 
pressure they may exercise upon them, or the 
nourishment they may withdraw ;—whilst the 
latter, having once made their appearance in 
the body, tend to reappear at distant parts (even 
after the original growth has been removed), 
induce a complete change of structure and of 
actions in the organs in which they are de- 
veloped, and exert a very depressing influence 
upon the bodily system at large. 
The non-malignant growths may present 
various characters, intermediate between those 
of the tissues they replace, and those of malig- 
nant structures. In regard to their pathological 
cause, “we cannot at present go beyond the 
supposition, that they arise from altered vital 
properties in some of the molecules of the 
textures in which they are developed ; so that, 
instead of being assimilated to these textures, 
and conforming to the laws of their growth 
and decay, these molecules grow of themselves 
in modes more or less peculiar, and more or 
less independently of the influences of the 
adjoining living parts. Where these modes 
are less peculiar,and more dependent upon the 
nutrition of the adjacent structures, the growths 
3c 2 
