398 



SCIENCE 



[N. ?. Vol. XLAII. No. 1216 



ganglia in the body cavity and elsewhere, to- 

 gether with many of their gross connections. 



This method has also 1 'en proved to be of 

 advantage in the study of glands. Here, again, 

 the breaking down of connective tissue seems 

 to be the chief factor. Glands are thus 

 separated from other organs, the outlines of 

 their lobes come into view, ducts are released 

 from their envelopes and the nerve supply, 

 wherever meduUated, can be easily traced. In 

 the study of glands the color effects from this 

 treatment, as in the case of nerves, are help- 

 ful to investigation. 



It is apparent that a readily applied 

 anatomical method which brings parts to dis- 

 tinct view with little or no dissection is of 

 wide usefulness in embryology. A statement 

 by Professor Mead of the applicability of this 

 method to pig embryos will be found below. 



One of the greatest advantages of the 

 method, whether applied to nerves, muscles 

 or glands, is finally to be mentioned, namely, 

 it permits the use of the camera lucida for 

 drawing. It has been found entirely practi- 

 cable to mount a camera lucida (Abbe type) 

 over the right eye-piece of a binocular micro- 

 scope and to reduce the field of the left eye- 

 piece by a superposed cylinder 1.8 cm. long, 

 the upper aperture of which is 3 mm. in diam- 

 eter. This arrangement prevents the observer 

 from shifting the eye to a different view from 

 the one desired and from thus throwing out 

 of position the lines already drawn, as the 

 work proceeds. S. E. Longwell 



Arnold Biological Laboratory, 

 Brown University 



application of the method to the dissection 



OF PIG EMBRYOS 



The method here described by Mr. Long- 

 well has proved to be very valuable in prepar- 

 ing pig embryos for general dissection. Em- 

 bryos from 13 mm. to nearly full term were 

 treated with about 1 per cent. HCl and either 

 kept for 2 or 3 days in the refrigerator or, when 

 weather was cold, out of doors and sometimes 

 frozen. In some cases they remained in the 

 refrigerator for a month. Some of the spec- 

 imens were dissected immediately after rins- 



ing the acid off with water and others were 

 kept in about 1 per cent, solution of carbolic 

 acid. 



The treated specimens retain nearly the 

 texture and pliability that they had when 

 taken from the uterus. The muscles are 

 rendered slightly more opaque rather than 

 transparent as in the guinea pigs prepared by 

 Mr. Longwell. The nerves, therefore, do not 

 present the striking contrast to muscles in 

 color which his specimens show. In case of 

 the embryos, however, the slight opacity of 

 the muscles is rather an advantage. 



The advantages of the method as applied 

 to the embryos are the complete lack of 

 rigidity or brittleness, the extraordinary ease 

 with which the adjacent parts can be separated 

 when the connective tissue is partly dis- 

 solved. The epithelium separates from the 

 true skin and the latter from the superficial 

 fascia with the greatest ease. The skin 

 muscles, for example, the platysma and facial 

 and auricular muscles, show with diagram- 

 matic clearness. The deeper muscles retain 

 sufficient strength for purposes of dissection. 

 The nerves retain their strength entirely and 

 are white. It is easy to follow them to their 

 minutest branches. The cerebrospinal and 

 sympathetic ganglia are also tough. 



The facility that the method lends to the 

 dissection of embryonic glands and ducts is 

 equally delectable. The ducts of the sub- 

 maxillary and parotid in a pig of 100 mm. 

 can still be followed to their ultimate branches. 

 The liver becomes soft but when pinched be- 

 tween the fingers and washed the branches of 

 the vessels, the gall bladder, cystic and hepatic 

 ducts, etc., are left and the relation of the 

 omenta and the foraraen of Winslow are 

 most satisfactorily exposed. 



Tendons, fascia, the peritoneum, blood ves- 

 sels and meninges retain sufficient toughness 

 for satisfactory dissection. The brain and 

 cord are of better , texture and color than in 

 either fresh specimens or those prepared in 

 formalin or fixing agents followed by alcohol. 



In general Mr. LongweU's method is invalu- 

 able in the dissection of pig embryos. 



A. D. Mead 



