126 OUTLINES OF BACTERIOLOGY 



Fraenkel's 2^fi^umococGus is a small oval coccus about I fi across its 



longer side. The cocci are generally in pairs (Fig. 79), but sometimes 



there may be 4-10 cocci attached together. The 



^ term " pneumococcus " was a temporary one, and 



^ ^ it is now usual to replace it by the generic name 



^[^ ^^^ ^ " micrococcus," to which group the organism 



^ belongs. In true croupous pneumonia this 



^ species is by far the most frequent organism 



^"- ^°- m^Soous.''' ^°'"' that is present. The free ends of a group of 



attached cocci are often pointed in the form of 



a lancet. Each group has usually a transparent covering enveloping 



and protecting it. This covering or capsule forms a kind of halo round 



the group of cocci. 



Friedlander's Pneumdbacillus is rod-shaped with blunt rounded ends. 

 It agrees with Fraenkel's pneumococcus in its capsule formation and 

 in the tendency of its individuals to form pairs. Its occurrence is, 

 however, much rarer, being present in only about 5 per cent, of the 

 cases of pneumonia, in fact, its causative connection with this disease is 

 very doubtful. 



Fraenkel's pneumococcus, which has an undoubted causal connection, 

 has been isolated and closely investigated. The name pneumotoxin has 

 been given to the poison secreted by this microbe. When a patient 

 succumbs to this disease, the immediate cause of death is heart failure 

 and general nervous depression, resulting from the pneumotoxin, rather 

 than suffocation resulting from the interference with the functions of 

 the lungs. Animals can be rendered immune against this microbe by 

 being inoculated with a mild form of the toxin. 



In addition to the species that have been described, many others 

 are known, which have some connection with one or other of the 

 various diseases with which we are inflicted. 

 In most of these cases, however, very little is 

 known of causative organisms, and their power 

 of bringing about disease is dependent in many ^f§M^ 

 cases on the co-ordination of other bacteria, ^* 9t^^^ 



that is, there must be symbiosis between two ^ * 



or more organisms. This makes investigation fiq. so.— staphylococcus 



° 11^1 pyogenes aureus. 



more difficult. Again, many of the less harmful 



diseases are due to the toxins secreted by Staphylococci. These 

 organisms are found associated with abscesses, pustules on the skin, 

 carbuncles, boils, and also some catarrhs and ulcers. The best known 

 of these bacteria is Staphylococcus pyogenes aureus (Fig. 80). This 



'^ 



