DIPHTHERIA. 3OI 



bacillus, which appears to be the only organism of all those 

 found in the membrane that can form colonies visible 

 to the naked eye in twenty hours. Such colonies grow as 

 small rounded greyish white points, the centre of each of 

 which is more opaque than the periphery ; they spread 

 rapidly, form greyish rounded discs, and continue to develop 

 so quickly that they are very evident before the other 

 organisms have begun to form a colony at all visible to the 

 naked eye. From these points, inoculations on to blood 

 serum may be made. 



Probably the best nutrient material for the diphtheria organism is that 

 recommended by Loffler ; it is composed of three parts of blood serum, 

 one part of neutralized broth, to which has been added i per cent, of pep- 

 tone, . S per cent, of common salt, and i per cent, of grape sugar. Ordinary 

 blood serum comes next, and then agar-agar j^Uy. On E^ar plates the 

 colonies situated in the substance are coarsely granular, dark brown, and 

 somewhat rounded or oval ; although where several colonies have run to- 

 gether they may give rise to somewhat irregular outlines. The superficial 

 colonies are much lighter in colour, are not so dense, and have an irregular 

 scalloped border. 



These cultivations are found to be made up of bacilli 

 similar to those described by Klebs ; they are not quite so 

 long as the tubercle bacillus, but are rather thicker, the 

 extremities, which are more deeply stained than the central 

 portion, are often slightly enlarged. In older cultivations 

 the rods are not uniformly coloured, and there may be seen 

 in the substance of the protoplasm bodies which somewhat re- 

 semble spores. It was soon noticed that with this inequality 

 of staining, certain other changes in the organism might be 

 met with ; so-called involution forms make their appearance. 

 In these the bacilli are cut up into small rounded masses of 

 protoplasm, some of which have a less diameter than that of 

 the bacillus, whilst ethers may be considerably larger and are 

 oval in shape. These involution or degenerate forms soon 

 make their appearance where the conditions for the growth 

 and development of the bacillus are unsatisfactory, and it is 

 supposed that many of the failures to find the typical rod- 

 shaped bacilli in old diphtheritic membranes are due, in some 

 measure, at any rate, to the occurrence of these involution 

 forms in the later stages of the disease, where the membrane 

 is invaded by putrefactive and other organisms which inter- 

 fere with the growth of the specific bacillus. It is also 



