BY DR. KLEIN. 23 



its aid, it is possible to continue the observation for a long pe- 

 riod. It is this which is employed by Sanderson and Strieker 

 for the study of the circulation in mammalia. For our present 

 purpose we do not require the whole apparatus, so that it is 

 only necessary to refer to those parts of it which are shown in 

 Fig. 3. 



In the employment of this apparatus several difficulties are 

 encountered. For instance, the temperature of the water re- 

 ceptacle ; .s only in part controlled by the regulator. Then, 

 again, the temperature of the stage is subject to variation ac- 

 cording to the rate at which the water flows into and escapes 

 from it; so that, if great care be not taken in the adjustment, 

 constancy cannot be relied on. Another practical difficulty 

 lies in the fact that the temperature of the water in the recep- 

 tacle is different from that in the stage, the rate of flow being 

 so inconsiderable that there is necessarily a great loss of heat 

 by radiation from the metal surface. If the stage be not fitted 

 with a thermometer, this difference of temperature may be de- 

 termined, once for all, by comparative measurements, so that 

 the true temperature of the stage can then be known at any 

 time by deducting the ascertained loss of heat, i. e., the ascer- 

 tained difference above referred to, from the temperature to 

 which the regulator is adjusted. 



Method of varying the temperature rapidly. In 

 connection with this apparatus, it is convenient to describe 

 the method employed for subjecting a preparation to sudden 

 alterations of temperature. With this view the following con- 

 trivance is used : A clip is placed on the tube leading from the 

 water receptacle (C f , Fig. 3), by means of which the access of 

 warm water to the stage may be interrupted. The end of the 

 escape-tube (D) is then allowed to dip into a vessel of cold 

 water. This done, cold water may be readily introduced into 

 the stage, so as to cool it suddenly, by suction through the 

 tube ((7), which must be provided with a branch (not shown 

 in the figure) between the clip and the stage, for the purpose. 

 This, of course, at once lowers the temperature. To effect a 

 sudden rise, all that is necessary is to open the clip. For short 

 experiments, it is not necessary to have a water receptacle spe- 

 cially constructed for the purpose ; a large flask, supported 

 over a lamp, and without a regulator, may be substituted for 

 it, provided that, in addition to the discharge-tube, a thermom- 

 eter is passed through the cork, in order that the variations of 

 temperature maybe observed, and the application of heat mod- 

 ified accordingly. 



Effects of Warmth on the Colorless Corpuscles. 

 We now return to the study of the drop of newt's blood, in- 

 closed between two cover-glasses, with which we were occu- 

 pied. On subjecting the preparation to a temperature of 38 



