CH. xxrii.] IN TKIINAL SECRKTION. 321 



cease altogether if any of the links in the chain break 

 down. 



In unravelling the part which the ductless glands play in this 

 cycle, it is at present impossible in many cases to state precisely 

 what the particular function of each is ; all one can say is, when 

 the gland is removed or its function interfered with, that the 

 metabolic round is broken somehow, and that this upsets the 

 whole of the machinery of the body. The difficulty of investi- 

 gating this subject is increased by the fact that it is impossible 

 to get the intemal secretion in a state of purity and examine it ; 

 it is always mixed with, and masked by, the lymph or blood into 

 which it is poured. 



In spite of this, however, our knowledge in this branch of 

 physiology is increasing, particularly in connection with some of 

 these ductless glands. The methods of investigation which have 

 been employed are the following : 



1. Extirpation. The gland in question is removed, and the 

 effect of the absence of the internal secretion noted. 



2. Disease. In cases where the function of the gland is in 

 abeyance, owing to its being diseased, the symptoms are closely 

 observed. 



3. Injection of Extracts. The gland is taken in a fresh condi- 

 tion ; an extract is made of it, and this is injected into the 

 circulation of healthy animals, and into that of those animals 

 from which the gland has been previously removed, and the effects 

 watched. 



4. Transplantation. After the gland is removed and the 

 usual effect produced, the same gland from another animal is 

 transplanted into the first animal and restoration of function 

 looked for. 



The case of the lymphatic glands we have already studied ; 

 they form an internal secretion which consists of lymph-cells, and 

 these furnish the blood with its most important supply of colour- 

 less corpuscles. Removal of lymphatic glands is not fatal, as 

 the other lymphatic glands and other col lections of lymphoid 

 ti>-ue that remain behiqd carry on the work of those that are 

 removed. 



The iiiteinal >eci-etion theory ( the ductle-s glands is that which is most 

 in vogue at pre>ent. It >hould he mentioned, however, that there is another 



'I ry. which may be called the tiutn-iiitii.rii-iitnni theory. According to this 



view the gland i- excretory (i.e., gets rid of waste and harmful materials) 

 rather than -'Tetory (i.e.. production of something useful to the organism). 

 \Vhen the gland is removed. ! he waste products therefore accumulate and 

 produce harmful results. It is possible that as our knowledge increases it 

 may l>e found in certain cases that both these theories may be in part true. 



K.P. T 



