GENERAL FUNCTIPNS OF NERVOUS SYSTEM. 473 



have much less disposition to pass off by this secretion ; and they are 

 consequently to be preferred during lactation. 



839. From the close correspondence which exists, between the ele- 

 ments of the Milk and those of the Blood, it is evident that we cannot 

 expect to trace the existence of the former, as such, in the circulating 

 current. It is interesting, however, to remark, that a preparation 

 appears to be. taking place in the laboratory of the system, for the pro- 

 duction of this secretion, long before the period of parturition. The 

 Urine of pregnant women almost invariably contains a peculiar sub- 

 stance termed kiestine, which is nearly related to caseine, and which 

 disappears from the urine as soon as lactation has fully commenced. 

 It would seem, therefore, that a compound of this nature is in course 

 of preparation during pregnancy; and that it is eliminated by the 

 kidney, until the Mammary Gland is prepared for the active perform- 

 ance of its functions. That the Kidney may relieve the system from 

 the accumulation of other constituents of the mammary secretion, 

 appears from a case recently put on recond ; in which the urine of a 

 parturient female, who did not suckle her infant, was found to contain 

 a considerable quantity of butyric acid, during several days. There can 

 be no doubt that, in ordinary states of the system, this secretion can- 

 not be required for the depuration of the blood, since it does not occur 

 in the male at all, and is present in the female at particular times only. 

 But these facts afford ground to believe that, when the process is going 

 on, certain products are generated in the system, which are not found 

 there at other times. And it is quite certain that the sudden checking 

 of the secretion, or the reabsorption of the fluid already poured out, 

 occasioning an accumulation of these substances in the circulating cur- 

 rent, may give rise to very injurious consequences. Some very curious 

 instances are on record, in which a transference of the secreting power 

 to some other surface has taken place under such circumstances ; so as 

 to relieve the system from the accumulation in question. 



CHAPTER XII. 



; 

 OF THE NERVOUS SYSTEM AND ITS ACTIONS. 



1. General View of tlie operations, of which the Nervous System is the 



instrument. 



840. WE have now considered the entire series of those operations, 

 which make up the vegetative or organic life of the Animal ; including those 

 functions by which the germ is prepared, by which it is nourished until 

 it can be left to its own powers, by which its continued development is 

 effected until the fabric characteristic of the adult has been built up, 

 and by which the normal constitution is maintained through a length- 

 ened period, so long as the necessary materials are supplied, and no 



