SCOTT, STUDY OF CHANGES IN MUSTELUS CANIS 



21 



1.034-f-. The curve C — D represents the freezing point of the blood at 

 the different concentrations represented by the curve A — B. It is con- 

 structed by drawing a line through the following points : C = the A of 

 the blood at the death of the organism in fresh water ; N, the A of normal 

 blood; D, the A of the blood at the death of the animal in the concen- 

 trated solution, having a specific gravity of 1.034-|- and a A of 2.60°, the 

 effect of which has been described in this section of the pajDer; E, the A 

 of blood of Squalus acanthias in harbor water which has a A of about 

 1.00°. 



A further account of this is given later (on page 31). That the oper- 

 ation of destroying the cord did not modify the results is strongly indi- 

 cated by the folloAving instance : A large Mustelus canis was operated on 

 in an attempt to collect a sample of its 

 urine. The spinal cord was destroyed in 

 the manner already indicated. The ab- 

 dominal cavity was opened, the rectum 

 was ligated and a large glass tube was fas- 

 tened in the cloaca. The animal was then 

 placed on a support in the sea-water in 

 such a way that the head as far back as 

 the last gill slit was under water. The 

 abdominal incision was closed and the 

 surface of the body was kept moist with a 

 cloth wet with sea-water. At the end of 

 twenty-four hours the fish was still alive 

 and breathing normally. When the peri- 

 cardium w^as opened, the heart was seen to be beating regularly. Figure 

 4 is a record of the respiration at the end of twenty-four hours, the time 

 record indicating intervals of two seconds. Although the experiment 

 was a failure as far as its primary purpose was concerned, it proved that 

 the above operation in itself is no cause of immediate death. Sheldon 

 ('09) has found that Mustelus may live for a week after a similar de- 

 struction of the cord. Parker ('10) has called attention to "the ease 

 with which this fish resists the adverse effects of operations." 



In a series of earlier experiments, the results of which are given in 

 Table VI, on the effect of immersion in fresh water on the freezing point 

 of the blood, I first defibrinated the blood, then centrifuged it, and used 

 the serum for the determination of the freezing point. About 10 to 15 c. c. 

 of serum was used for each determination. 



In these preliminary experiments, blood was drawn from each specimen 

 but once. In the case of the specimens immersed in fresh water, the 



Fig. 4. — Resinratory movements 

 in Mustelus. 2.'/ hours after de- 

 struction of si)inal cord. 



