INTESTINAL NUTRITION IN THE OPOSSUM 343 



The whole specimens, which had been fixed in Bouin's fluid, 

 were later run down from 80 per cent alcohol to water — using a 

 fluid-changing device by which one solution was added to the 

 other drop by drop. The apparatus was provided with a glass 

 stirring plunger which was raised and lowered by a cam-shaft,, 

 and an overflow-siphon controlled the volume of the solution 

 surrounding the specimen. After staining in alum-cochineal, the 

 specimens were carried back to 80 per cent alcohol, making use of 

 the same device to insure slow^ interchange of fluids. The 

 abdominal wall was then dissected off so that the external form 

 and position of the viscera could be studied. Next the liver, 

 stomach, and intestines were removed in one piece, and later, 

 in order not to injure the other structures, the liver was dissected 

 off with needles. As a means of recording the appearance of the 

 dissections at the various stages, stereophotographs were made 

 during the progress of the work. The block to be sectioned 

 included the stomach and intestines; it was embedded in paraffin 

 and cut into a series of sections 5/x thick, by Professor Ruber's 

 water-on-the-knife method. The sections were stained with 

 Mallory's connective-tissue stain. The use of the cochineal was 

 advantageous in that the embryos were satisfactorily stained for 

 preliminary dissections before imbedding or for subsequent 

 dissections; the stained embryos could also be photographed well; 

 and in the sections the nuclear detail was better shown than with 

 Mallory alone. The latter stain was very useful for showing 

 differentiation among the various tissues. This method of stain- 

 ing the whole embryos in alum-cochineal and the sections with 

 Mallory's connective-tissue stain has been used on specimens 

 of various ages and has proved to be of value. Several series 

 of sections were prepared and used for reference, but the chief 

 observations in this study were made on an embryo of few hours 

 before birth and on a pouch-young about three days old. 



THE AMEBICAN JOURNAL OF ANATOMY, VOL. 28, NO. 2 



