396 



SCIENCE 



[N. S. Vol. XLVII. No. 1216 



parts studied, with tlieir relations to the otlier 

 parts, without disturbing the natural mobility 

 of the tissues as a whole. Such a fluid should 

 reduce the work of dissection so that a mini- 

 mum of disturbance is necessary in order to 

 reach the parts under investigation. 



A most serious objection to formalin is the 

 adhesive effect it has upon tissues, so that 

 parts are not readily separable. Muscles are 

 stuck together in a more or less brittle or 

 fused mass and the nice mobility of tissues 

 observable in a fresh specimen is wholly de- 

 stroyed. Resultant color changes, too, are 

 such as to make dissection more difficult, for 

 muscles are altered from their characteristic 

 reddish to whitish tints, and it is consequently 

 impossible or exceedingly difficult to trace the 

 smaller nerves to regions of their ultimate 

 distribution. 



Formalin adds to, rather than subtracts 

 from, the amount of dissection required, on 

 account of the care necessary in avoiding 

 severance of parts to be left intact. 



After giving formalin a thorough trial as 

 an aid for studying the peripheral nervous 

 system it was discarded altogether and the use 

 of fresh specimens employed as a substitute 

 method. But while fresh material is much 

 easier to work upon, the finer nerves are even 

 less distinct than they are after the use of 

 formalin. Moreover, fresh tissues soon begin 

 to deteriorate and the animals become unfit 

 for further use. Pieces of ice kept constantly 

 near, or upon, the material were then tried, 

 with some improvement. Although the ani- 

 mals can be kept for a period of three weeks 

 by resorting to the ice chest, the dissections 

 are not satisfactory. The reason for this is, 

 not only because too much mechanical effort 

 is necessary to segregate the parts, but also 

 because the smaller nerves are not brought 

 clearly to view. 



A temporary preservative, and, what is of 

 much more importance, an almost ideal pre- 

 parative, for the investigation of the periph- 

 eral nervous system, muscles and glands, is 

 found in hydrochloric acid. 



The fresh animals may be first put in a 5 

 per cent, solution of hydrocJiloric acid ice- 



water and left for twenty-fovu: hours. They 

 may be skinned or not, as the problem in 

 hand requires, but the body and chest cavities 

 should in any case be opened to allow the 

 fluid to penetrate through the tissues. 



In preparing specimens for work on the 

 cutaneous nerves it is necessary, of course, to 

 leave undisturbed whatever portions of skin 

 are to be studied; otherwise, it is best to re- 

 move the entire skin. 



After treatment with hydrochloric acid the 

 animals are washed in the coldest water ob- 

 tainable from the faucet, and put in recep- 

 tacles deep enough so that the material can 

 be kept covered with ice-water or at least 

 cold water. These receptacles are then stored 

 in the refrigerator when the specimens are not 

 in use. 



In using animals so prepared it is found 

 practical to wash them first in running water, 

 leaving the pan partly filled, and then to add 

 pieces of ice sufficient to surround the speci- 

 men while observation and dissection are go- 

 ing on. In tracing the smaller nerve divi- 

 sions, details are brought out better if, oc- 

 casionally, dilute acid is added, by means of 

 a pipette, directly to the parts under con- 

 sideration, since by this treatment the trans- 

 parency of the muscle fibers is increased. 



Guinea pigs treated by the above method 

 were found to be in excellent condition for 

 following medullated nerve fibers far into the 

 tissues which they supply. 



The 5 per cent, acid solution increases the 

 whiteness of the nerves bringing them into 

 sharp contrast with the natural reddish, or 

 reddish-brown, back-ground of muscles, but 

 if much stronger acids are used, even 10 per 

 cent., it tends to whiten the muscles and dis- 

 solve the fibers without improving the color 

 of the nerves. 



Animals are also put in good condition for 

 dissection if treated with a 6 per cent, acid 

 solution. If a specimen is to be used during 

 a long period it is better to give an initial 

 twenty-four hour treatment in an acid solution 

 not stronger than 3 per cent, and subsequent 

 immersions in the same strength of acid for 

 shorter periods. In any case the water left 



