CHEMICAL CONSTITUTION AND PHARMACOLOGICAL ACTION 417 



In my opinion, however, this general distribution is a very im- 

 portant problem, for just these facts furnish the most valuable in- 

 formation concerning the chemical functions of the organs, and of 

 the elements which compose them. At present this problem can 

 only be solved by the employment of dyes whose distribution we can 

 readily follow both macroscopically and microscopically. It is to be 

 deplored that these investigations, which possess such a high didactic 

 value should thus far have found so few adherents; they are only 

 exceptionally studied and then for some particular purpose. 



If rabbits are injected with dyes it will be found that even macro- 

 scopic study yields most interesting pictures. There are certain 

 dyes, although not very common, which stain only a particular tissue, 

 e.g. fat tissue; these are called " monotropic." Usually a dye 

 possesses an affinity for a number of systems of organs, although 

 frequently it then happens that one particular organ is stained in 

 an especially conspicuous manner. Very often one finds that the 

 maximum staining is in the kidney (especially in the cortex) and in 

 the liver. Other dyes, such as acridinorange and dimethylamido- 

 methylene blue, exhibit their stain particularly in the thyroid gland ; 

 still others, as dimethylphenylene green, stain especially the fat tissue; 

 some, such as alizarin blue, the submaxillary gland, etc. 



Alizarin blue, besides staining brain and kidneys, stains the sub- 

 maxillary gland with especial intensity. As examples of polytropic 

 stains we may mention neutral red and a basic dye, brilliant cresyl 

 blue, for these stain the majority of body parenchyma intensely and 

 apparently uniformly. It is particularly significant that the majority 

 of basic dyes which stain the brain are also stored up by fat tissue. 

 As we shall soon see neurotropism and lipotropism are related to 

 one another. 



The variation in the localization of dyes frequently corresponds 

 to certain peculiarities in their excretion; the chief points of excre- 

 tion are probably kidney cortex, liver, and intestine. In contrast 

 to the great majority of dyes which, like methylene blue, fuchsin, 

 alizarin, indigo carmine, and many others, gain access to the urinary 

 secretions very easily, there are several which seem incapable of 

 doing this and which therefore seem by preference to be excreted 

 through the bile or through the intestinal juices. An example of 

 this is benzopurpurin, a very large-moleculed cotton dye which is 

 made from diazotated toluidin and naphylaminsulfonic acid. 1 



1 It is possible that this phenomenon can be fully explained by this that we 



