PROBLEM 3 How Have Recent Discoveries Changed 



Some of Our Ideas About Disease? 



Advances in the germ theory. At one 



time it looked as though knowledge of 

 the germ theory of disease and of active 

 and passive immunization would make 

 it possible to conquer every infectious 

 disease fairly soon. Unfortunately, later 

 research showed that facts were not so 

 simple as had been believed. For example, 

 \\'hile it has long been known that pneu- 

 monia is caused by a spherical germ 

 (pneumococcus — new-mo-cock'us), fur- 

 ther study showed about 32 different 

 strains of this germ. Thev all look alike 

 under the microscope and they all cause 

 the same general type of disease which 

 the doctor calls pneumonia but they dif- 

 fer in their activities. And the treatment 

 that may help against one strain may not 

 help against another. Physicians now 

 speak of Type I, Type II, and Type III 

 pneumonia germs. What was once called 

 Type IV is known to be a group of 

 about 29 strains. And what is more, some 

 kinds of pneumonia are caused by other 

 bacteria as well as by viruses. 



The different strains of a germ differ 

 in their effect on the patient. One strain 

 may be weak or nonvirulent; another 

 may be very virulent. They may even 

 grow differently on nutrient ag^ar. In the 

 case of typhoid and some other germs, 

 the virulent strain forms smooth, round 

 colonies. The weak strain forms roui^h 



colonies. The difference is so marked 

 that bacteriologists have come to speak 

 of 5" and R strains. 



The different strains of a germ often 

 change. In one experiment a harmless 

 germ found in drinking water was in- 

 jected into an animal in the laborator^\ 

 Later, M'hen it was recovered from the 

 animal, it had become virulent. In an- 

 other case, nonvirulent Type I pneu- 

 monia germs were injected into mice to- 

 gether with dead Type II germs. The 

 germs later found in the mice were a 

 virulent Type I strain! Evidently, we are 

 still far from having solved all the prob- 

 lems of infectious disease. 



Learning more about antibodies. Bac- 

 teriologists are now attempting to dis- 

 cover the chemical nature of various 

 antibodies. They hope to be able to man- 

 ufacture antibodies in a test tube, instead 

 of merely relying on an animal's body to 

 manufacture them. A beginning has been 

 made at the California Institute of Tech- 

 nology. The Type III pneumonia germ 

 has a coating which contains a special 

 kind of sugar. When this sugar is added 

 to one of the proteins of blood plasma, 

 heated, and then slowly cooled, the pro- 

 tein changes into a new protein which 

 acts as an antibodw While this antibody 

 has not \'et been used in disease preven- 

 tion, this is a most important discovery. 



