100 MICROSCOPICAL RESEARCH IN THE 



not, like chromic solutions, harden the object, but simply kills the 

 cells. 



As this fluid penetrates thick chitine with difficulty, it is neces- 

 sary, in order to obtain good preparations of larger Isopoda, 

 insects, etc., to cut open the body and fill the body-cavity with the 

 liquid by means of a pipette. In larger objects care should be 

 taken to loosen the internal organs so that the fluid may find easy 

 access to all parts. 



The fluid should be applied as soon as the body is opened, so 

 that the blood may not have time to coagulate and thus bind the 

 organs together. A large quajitity of the fluid should be used, and 

 it must be changed as often as it becomes turbid. The same rule 

 holds good in the use of all preservative fluids. It is well also, 

 especially with larger objects, to give the fluid an occasional 

 stirring up. 



In order to avoid shrinkage in removing small and tender 

 objects from the acid to the alcohol, it is advisable to take them 

 up by means of a pipette or spatula, so that a few drops of the 

 acid may be transferred along with them. The objects, sinking 

 quickly to the bottom, remain thus for a short time in the medium 

 with which they are saturated, and are not brought so suddenly 

 into contact with the alcohol. In a few minutes the diffusion is 

 finished ; and they may then be placed in a fresh quantity of 

 alcohol, which must be shaken up frequently and renewed from 

 time to time until the acid has been entirely removed. 



The sulphuric acid contained in this fluid causes connective 

 tissue to swell, and this fact should be borne in mind in its use 

 with vertebrates. To avoid this difficulty, Kleinenberg has recom- 

 mended the addition of a few drops of creosote, made from 

 beechwood tar, to the acid. According to Dr. Mayer's experience, 

 however, the addition of creosote makes no perceptible difference 

 in the action of the fluid. 



This fluid must not be used with objects {e.g., Echinoderms) 

 possessing calcareous parts which it is desired to preserve, for it 

 dissolves carbonate of lime and throws it down as crystals of 

 gypsum in the tissues. For such objects — 



