300 ALWIN M. PAPPENHEIMER 



MATERIAL AND TECHNIC 



The glands were obtained during the months of July, August 

 and the early part of September from freshly caught specimens 

 of Rana clamata; a few also from spotted frogs shipped from a 

 distance and showing in consequence of the prolonged starvation, 

 marked involutional changes. In addition to the usual histo- 

 logical methods a variety of granule stains were used: Altmann's 

 acid fuchsin, as originally described and as modified by Lane; 

 Bensley's neutral gentian violet (1); Heidenhain's iron-alum 

 hematoxylin after fixation in Benda's modified Fleming's solu- 

 tion; and Benda's mitochondrial stain, used in the manner origi- 

 nally described by him and according to the modification sug- 

 gested by Meves and Duesberg (2). The clearest pictures were 

 obtained with the modified Benda method, although somewhat 

 varying appearances were often presented by sections prepared 

 with the same technic. 



The preparation of in vitro cultures has been so often described 

 that it is unnecessary to give the method again in detail. The 

 plasma was obtained directly from the frog's heart by aspiration 

 with an oiled needle or glass pipette. Hanging drop cultures 

 were kept at room temperature, as it was found that all the 

 elements rapidly degenerated when incubated at 37°. In study- 

 ing the reaction of the cells to various vital stains, dilute sterile 

 solutions -of the dye in Ringer's fluid were added directly to the 

 cultures. In this way, with the gradual diffusion of the dye 

 through the plasma, the reaction of individual cells could be 

 directly observed. In other cases, the vital stain was added to 

 the plasma before implanting the tissue, but under these condi- 

 tions, for reasons which will be discussed later, no growth was 

 observed. 



HISTOLOGICAL STUDY 



In the adult frog, the thymus is an elliptical, slightly flattened 

 yellowish body, from 2 to 4 mm. in length, situated on either 

 side beneath the angle of the inferior maxillary, and in close 

 relation to the glosso-pharyngeal nerve and the depressor man- 



