504 NUTRITION. 



tents. The form of the vesicles is naturally rounded or ovoid ; but in microscopical 

 preparations they are generally compressed so as to become irregularly polyhedrical. 

 The membrane sometimes presents a small nucleus attached to its inner surface. The 

 contents are, a minute quantity of an albuminoid fluid moistening the internal surface 

 of the membrane, and a mixture of oleine, margarine, and stearine, liquid at the temper- 

 ature of the body, but becoming harder on cooling. Little rosettes formed of acicular 

 crystals of margarine are frequently observed in the fat-vesicles, when the temperature 

 is rather low. 



The adipose vesicles are collected into little lobules, from ^ 7 to i f an incn in diame- 

 ter, which are surrounded by a rather wide net-work of capillary blood-vessels. Close 

 examination of these vessels shows that they frequently surround individual fat-cells, in 

 the form of single loops. There is no distribution of nerves or lymphatics to the ele- 

 ments of adipose tissue. It is seen by this sketch of the structure of adipose tissue, that 

 there is no anatomical reason for classing these vesicles with the ductless glands, as 

 is done by some physiologists. They undoubtedly, under certain conditions, have the 

 power of filling themselves with fat ; but it would be no more appropriate to call fat 

 a secretion than to apply this term to the development and nutrition of the muscular 

 substance within the sarcolemma. 



Conditions which influence Nutrition. We know more concerning the conditions 

 that influence the general process of nutrition than about the nature of the process itself. 

 It will be seen, for example, when we come to study the nervous system, that there are 

 nerves which regulate, to a certain extent, the nutritive forces. We do not mean to 

 imply that nutrition is effected through the influence of the nerves, but it is the fact that 

 certain nerves, by regulating the supply of blood, and perhaps by other influences, are 

 capable of modifying the nutrition of parts to a very considerable extent. 



In discussing the influence of exercise upon the development of parts, we have shown 

 that this is not only desirable but indispensable ; and the proper performance of the func- 

 tions of nearly all parts involves the action of the nervous system. It is true that the sep- 

 arate parts of the organism and the organism as a whole have a limited existence ; but it is 

 not true that the change of nitrogenized, living substance into effete matter, a process that 

 is increased in activity by physiological exercise, consumes, so to speak, a definite amount 

 of the limited life of the parts. Physiological exercise increases disassimilation, but it also 

 increases the activity of nutrition and favors development. It is a favorite sophism to 

 assert that bodily or mental effort is made always at the expense of a definite amount of 

 vitality and matter consumed. This is partly true, but mainly false. Work involves 

 change into effete matter ; but, when restricted within physiological limits, it engenders 

 a corresponding activity of nutrition, assuming, of course, that the supply from without 

 be sufficient. Other things being equal, a man will live longer under a system of physio- 

 logical exercise of every part, than if he made the least effort possible. It is, indeed, 

 only by such use of parts that they can undergo proper development and become the seat 

 of normal nutrition. But, notwithstanding all these facts, life is self-limited. Unless 

 subjected to some process which arrests all changes, such as cold, the action of preserva- 

 tive fluids, etc., organic substances are constantly undergoing transformation. In the 

 living body, their disassimilation and nutrition are unceasing ; and, after they are re- 

 moved from what are termed vital conditions, they change, first losing irritability, or 

 becoming incapable of performing their functions, and afterward decomposing into mat- 

 ters which, like the results of their disassimilation, are destined to be appropriated by 

 the vegetable kingdom. Nutrition sufficient to supply the physiological decay of parts 

 cannot continue indefinitely. The wonderful forces in the fecundated ovum lead it 

 through a process of development that requires, in the human subject, more than twenty 

 years for its completion ; and, when development ceases, no one can say why it becomes 

 arrested, nor can we give any sufficient reason why, with a sufficient and appropriate 



