NUTRITION. 



755 



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 

 perfectly 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, 

 crude, 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 contiaction. 



Fig. 406.* 



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 

 aged 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 

 some of the same tubercle, separated and magnified 

 about 820 diameters. 



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 

 a great tendency to favour it ; so that a larger 

 quantity may be produced in the lungs, after a 

 pneumonia has existed for a day or two, than it 

 would have required years to generate in the 

 previous mode. But the character of the de- 

 posit still remains the same ; and its relation to 

 the plastic element of the blood is shown by the 

 interesting fact, of no unfrequent occurrence, 

 that, in a pneumonia affecting a tuberculous 

 subject, plastic lymph is thrown out in one part, 

 whilst 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. 



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 ; 

 and the perversion of the structure and func- 

 tions of the part renders it peculiarly suscep- 

 tible of the influence of external morbific 

 causes. These views, at which several recent 

 physiologists 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; wjiilst 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 



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