SACCHAROMYCES : AMOEJLIL 39 



among the bacteria, but they become so when vigorous growth and suitable 

 conditions of nourishment allow them to multiply rapidly. Such instances 

 as the yeasts and the mould-fungi, with their energetic chemical effects, 

 suffice to remind us that the bacteria are not alone in their performances. 



Some of these low organisms (22) are, like the bacteria, capable of pro- 

 ducing pathological effects, but it is very rarely that such cases present the 

 characters of a genuine infectious disease. Only within the last few years 

 has it become known that the yeast-fungi (Saccharomycetes^ see Chap. XIV) 

 are capable of developing pathological properties. Injection into animals 

 of pure cultures of different species of brewery and distillery yeasts gives 

 rise to processes having all the characters of true parasitic diseases, ending 

 in many cases with the death of the animal. The germs spread to distant 

 parts of the body and are found in all the organs as well as in the blood, 

 but the lesions produced have not been recognized as those of any known 

 disease in human beings. Still, an infection by yeast cells is just as con- 

 ceivable as by any other organisms. It has recently been suggested that 

 the various forms of cancer and similar neoplasms may be due to parasitic 

 saccharomycetes, and some investigators have announced the discovery of 

 such in stained sections. Unimpeachable results have however not been as 

 yet attained, and it has been shown in some cases that the supposed para- 

 sites were nothing but fragments of cells and nuclei of the tissues themselves. 

 The parasitic nature of tumours is indeed denied by some pathologists. 



The thrush fungus (Saccharomyces alb leans of some authors) found 

 on the buccal mucous membrane of children belongs possibly to the 

 saccharomycetes. Its elongated cells have much the appearance of 

 a yeast and they multiply by budding in the same way, giving rise to 

 mycelium-like masses which cover the culture fluid with a thick pellicle. 

 They set up, too, in suitable media (beer-wort) weak alcoholic fermentation. 

 Whether these masses are true mycelia or not is uncertain, and it is 

 therefore doubtful whether the fungus should be classed among the yeasts 

 or with such hyphomycctes as Oidiimi and Monilia Candida. 



Some of the closely allied group of Flagellata occasionally occur as 

 parasites or messmates in the animal body (e.g. MastigopJwra) which, as we 

 have seen, have alliances to bacteria, but it has not yet been demonstrated 

 that they are ever pathogenic. Trichomonas vaginalis is sometimes found, 

 associated with other micro-organisms, in the mucous secretion of the 

 vagina. A species called Trichomonas intestinalis has been found in the 

 intestine in cases of diarrhoea and cholera, and a similar species occurs 

 sometimes in the lung (sputum) in cases of bacterial infection. It is highly 

 probable that all these forms are merely harmless water organisms which 

 have found their way accidentally into the human body. 



Of more importance are some of the Amoebae, that group of naked 

 protozoa which move about by the protrusion and retraction of portions of 



