.*> BIOLOGY AND TECHNIQUE 



1659, and the Dutch linen-draper, van Leeuwenhoek, in 1875, actually 

 saw and described living beings too small to be seen with the naked 

 eye. There can be no doubt that the small bodies seen by these men 

 and their many immediate successors were, at least in part, bacteria. 

 And indeed the descriptions and illustrations of several of the 

 earliest workers correspond with many of the forms which are well 

 known to us at the present day. 



During the century following the work of these pioneers, the 

 efforts of investigators lay chiefly in the more exact morphological 

 description of some of the forms of unicellular life, already known. 

 Conspicuous among the work of this period is that of Otto Friedrich 

 Muller. In the generation following Miiller's work, however, a 

 marked advance in the study of these forms was made by Ehren- 

 berg, 1 who established a classification which, in some of its cardinal 

 divisions, is retained until the present day. 



Meanwhile the regularity with which these ' ' animalcula " or 

 "infusion animalcula" were demonstrable in tartar from the teeth, 

 in intestinal contents, in well-water, etc., had begun to arouse in the 

 minds of the more advanced physicians of the time a suspicion as to 

 a possible relationship of these minute forms with disease. The con- 

 ception of * ' contagion, ' ' or transmission of a disease from one human 

 being to another, was, however, even at this time, centuries old. The 

 fact had been recognized by Aristotle, had been reiterated by 

 medieval philosophers, and had led, in 1546, to the division of con- 

 tagious diseases by Fracastor, into those transmitted "per contac- 

 tum," and those conveyed indirectly "per fomitem." It was for 

 these mysterious facts of the transmissibility of disease, that clini- 

 cians of the eighteenth century, with remarkable insight, saw an 

 explanation in the microorganisms discovered by Leeuwenhoek and 

 his followers. 



In fact, Plenciz of Vienna, writing in 1762, not only expressed a 

 belief in the direct etiological connection between microorganisms 

 and some diseases, but was the first to advance the opinion that each 

 malady had its own specific causal agent, which multiplied enor- 

 mously in the diseased body. The opinions of this author, if trans- 

 lated into the language of our modern knowledge of the subject, 

 came remarkably near to the truth, not only as regards etiology and 

 transmission, but also in their suggestion of specific therapy. 



The conception of a "contagium vivum" was thus practically 



1 "Die Infusionstierchen, " etc., Leipzig, 1838. 



