THF NEW CELL DOCTRINE 



esting discovery that there axe disease causers which are in- 

 visible even with the microscope. In recent years we hear 

 more and more of the so-called invisible organisms. In re- 

 gard to this we must express our opinion with reservation, for 

 it is by no means demonstrated that we have to deal in this 

 case with actually living organisms. It is possible that we have 

 to do only with chemical ferments. We have not time, how- 

 ever, to enter upon this discussion. For 

 the present at least we must hold to 

 the opinion that vital phenomena can 

 appear only when the amount of living 

 substance is so great that it can be 

 seen with the microscope. In other 

 words, the minimum quantity of chem- 

 ical substance which can serve as the 

 basis of life is many times greater than 

 the minimum quantity of substance 

 which suffices for a chemical reaction. 

 Here we encounter a fundamental char- 

 acteristic of life To permit the activ- 

 ities which are characteristic for hfe to 

 go on we must bring together many sub- 

 stances which stand in very special 

 relations to one another. Hence the 

 assertion that hfe is only possible when these conditions are 

 fulfilled, and this requires that the total amount should be 

 so much that we can see it with the microscope. 



Cells have been considered for a long time as independent 

 bodies. Quite slowly this view has been changing. Many 

 years ago botanists made the observation that vegetable 

 cells may be united by fine threads of living substance. 

 Similar relations have been observed in animals. In the sev- 



FiG. 3. — Drawing to 

 show the size of bacteria. 

 Magnification 1000 (i mm. 

 of the picture =0.001). 

 A, smallest bacilli (influ- 

 enza) ; B, streptococcus 

 gracilis (round); C, largest 

 cocci; D, pus cocci; E, ba- 

 cillus megatherium; F, red 

 blood corpuscle; G, splenic 

 fever baciUus. — After H. 

 Jaeger. 



