610 RABIES AND THE NEGRI BODIES 



to the laboratory where the examination is to be made. During the 

 warm season the tin bucket should be surrounded by cracked ice. 

 These measures, however, are sufficient only when the package can 

 reach its destination, particularly in summer, in less than twenty-four 

 hours. If it has to be on the road longer, or if the weather is very 

 warm, it is better to take the brain out of the cranium. The entire 

 brain can then be placed in pure neutral glycerin and sent to the 

 laboratory. This method has been frequently recommended, but it 

 is almost impossible to find the Negri bodies in a brain that has 

 been preserved in glycerin. The following method is, therefore, better : 

 Take out the brain, divide into two equal halves. Place one half into 

 several times its bulk of pure neutral glycerin, the other half into a 

 strong formalin solution (1 part of formalin to 4 parts of water). 

 When the brain arrives at the laboratory, very small pieces, not more 

 than 1 square centimeter large and less than half a centimeter thick, 

 are cut out from the gray matter of the Ammon's horn, the region 

 of the fissure of Rolando and the cortex of the cerebellum of the 

 formalin preserved material. These pieces are placed in Zenker's 

 solution for a few hours, then washed rapidly in running water, 

 then placed for one hour in pure water-free acetone, which is changed 

 once, and then dropped into melted paraffin, sectioned, and stained 

 by the eosin-methylene-blue method. The fixation by Zenker's fluid 

 may even be left out and the sections can then be simply stained by 

 hematoxylin and eosin. The watery eosin solution should then be 

 somewhat stronger than when used for ordinary work in histology or 

 pathology. If the Negri bodies are found the other half of the brain 

 in glycerin is not needed, but if they are not found and the investigation 

 is to be carried on, an emulsion in physiologic salt solution is made 

 from the brain substance in glycerin and injected into rabbits by the 

 subdural method. This necessitates opening the cranium by trephin- 

 ing, followed by the subdural injection. (Details of this method of 

 inoculation are given below.) 



Are the Negri Bodies Protozoa? That the Negri bodies are indeed 

 protozoa is not accepted as an established fact by all observers, and 

 some hold that they are degenerative or other products of elements 

 of the central nervous system of the animal or person infected with 

 rabies. The main reason for this belief is the observation first made 

 by Remlinger and Riffat-Bey, and confirmed by others, that emul- 

 sions of the central nervous system frequently can be filtered through 

 Chamberland and Berkefeld filters without losing their infectiousness. 

 However, it must not be forgotten that there are very small Negri 

 bodies which are probably very plastic and which under pressure may 

 easily pass the pores of porcelain or clay filters. The preponderance 

 of evidence today appears to be in favor of the protozoan nature of 

 the Negri bodies. 



Peculiar Biological Properties of Neuroryctes Hydrophobias. If the 

 Negri bodies are protozoa, strict parasites which live and multiply in 



