POWERS OF RESISTANCE OF BACILLUS 359 



(Figs. 119, 120). They are at first fairly uniform in size and 

 shape, but later involution forms are present. Many are swollen 

 at their ends into club-shaped masses which stain deeply, and the 

 protoplasm becomes broken up into globules with unstained 

 parts between (Fig. 121). Some become thicker throughout, 

 and segmented so as to appear like large cocci, and others show 

 globules at their ends, the rest of the rod appearing as a faintly- 

 stained line. Occasionally branched forms are met with. The 

 bacilli are non-motile, and do not form spores. 



Staining. They take up the basic aniline dyes, e.g. methy- 

 lene-blue in watery solution, with great readiness, and stain 

 deeply, the granules often giving the metachromatic reaction as 

 described. They also retain the colour in Gram's method, 

 though they are more easily decolorised than the pyogenic cocci. 

 By Neisser's stain (p. 108) the granules are stained almost black, 

 the rest of the bacillary substance yellowish brown. 



Powers of Resistance, etc. In cultures the bacilli possess 

 long duration of life ; at the room temperature they may survive 

 for two months or longer. In the moist condition, whether in 

 cultures or in membrane, they have a low power of resistance, 

 being killed at 60 C. in a few minutes. On the other hand, in 

 the dry condition they have great powers of endurance. In 

 membrane which is perfectly dry, for example, they can resist a 

 temperature of 98 C. for an hour. Dried diphtheria membrane, 

 kept in the absence of light and at the room temperature, has 

 been proved to contain diphtheria bacilli still living and virulent 

 at the end of several months. The presence of light, moisture, 

 or a higher temperature, causes them to die out more rapidly. 

 Corresponding results have been obtained with bacilli obtained 

 from cultures and kept on dried threads. These facts, especially 

 with regard to drying, are of great importance, as they show that 

 the contagium of diphtheria may be preserved for a long time 

 in the dried membrane. 



Effects of Inoculation. In considering the effects produced 

 in animals by experimental inoculations of pure cultures, we 

 have to keep in view the local changes which occur in diphtheria, 

 and also the symptoms of general poisoning. 



As Loffler stated in his original paper inoculation of the 

 healthy mucous membranes of various animals with pure cultures 

 causes no lesion, but the formation of false membrane may 

 result when the surface is injured by scarification or otherwise. 

 A similar result may be obtained when the trachea is inoculated 

 after tracheotomy has been performed. In this case the 

 surrounding tissues may become the seat of a blood-stained 



