January 14, 1916] 



SCIENCE 



41 



was no whit more advanced in the middle 

 of the seventeenth century than in the time 

 of Aristotle. 



The Period of Leeuwenhoek. — The use 

 of the microscope in biological research 

 began in the seventeenth century; it 

 was the improvement of this new instru- 

 ment of investigation and its application 

 to the study of the reproductive substances 

 that furnished the first fundamental ad- 

 vance in the theory of reproduction at the 

 hands of Leeuwenhoek, viz., the discovery 

 of the spermatozoa* in 1677. 



the generation or procreation of the ovum. For 

 the functions of both are termed ' conceptions, ' 

 and both, although the primary sources of every 

 action throughout the body, are immaterial, the 

 one of natural or organic, the other of animal ac- 

 tions; the one (viz., the uterus) the first cause and 

 beginning of every action which conduces to the 

 generation of the animal, the other (viz., the brain) 

 of every action done for its preservation. And 

 just as a 'desire' arises from a conception of the 

 brain, and this conception springs from some ex- 

 ternal object of desire, so also from the male, as 

 being the more perfect animal, and, as it were, the 

 most natural object of desire, does the natural 

 (organic) conception arise in the uterus, even as 

 the animal conception does in the brain. 



"From this desire or conception, it results that 

 the female produces an offspring like the father. 

 For just as we, from the conception of the 'form' 

 or ' idea ' in the brain, fashion in our works a form 

 resembling it, so, in like manner, the ' idea ' or 

 'form' of the father existing in the uterus gen- 

 erates an offspring like himself with the aid of 

 the formative faculty,' impressing, however, on its 

 work its own immaterial 'form' " (from William 

 Harvey, "On Conception," 1651). 



* This discovery is sometimes credited to Hamm, 

 described as a student of Leeuwenhoek 's. The 

 latter himself describes the occurrence as follows 

 (Phil. Trans., 1678, containing a letter from L. 

 dated November, 1677) : A certain Professor 

 Cranen, who had frequently visited Leeuwenhoek 

 for microscopical demonstration, requested by let- 

 ter that he should give Dominus Hamm, a relative 

 of his, some demonstrations of his observations. 

 On his second visit D. Hamm brought in a glass 

 vial some seminal fluid and stated that he had ob- 

 served living animals in it ; Leeuwenhoek confirmed 



This discovery aroused the greatest in- 

 terest in scientific circles ; a number of in- 

 vestigators repeated the observations and 

 a spirit of speculation which led to wild 

 flights of the imagination was aroused. 

 Leeuwenhoek had soon to defend his pri- 

 ority in the matter and to protest against 

 certain very imaginative views. Thus in a 

 letter dated June 9, 1699,^ he defends his 

 priority and combats the notion that the 

 human form can be observed in the sper- 

 matozoa. He inveighs especially against a 

 certaiu Dr. Dalen Patius, who claimed to 

 have seen the human form, 

 the two naked thighs, the legs, the breast, both 

 arms, etc., the skin being pulled up somewhat 

 higher did cover the head like a cap. 



Leeuwenhoek states that he can find 

 nothing of the sort, but he adds : 



I put this down as a certain truth, that the 

 shape of the human body is included in an animal 

 of the masculine seed; but that a man's reason 

 shall dive or penetrate into this mystery so far, 

 that in anatomizing one of these animals of the 

 masculine seed we should be able to discover the 

 entire shape of the human body, I can not com- 

 prehend. 



In a letter dated two weeks later he dis- 

 tinguishes two sorts of these animalcules, 

 and concludes that the one sort is male and 

 the other female. 



this observation and repeated it many times. In 

 this letter he gives a fair description of the sper- 

 matozoa, their form, size and movements and 

 stated that he had observed them three or four 

 years previously and mistaken them for globules. 

 He did not at this time speculate as to the meaning 

 of the spermatozoa, but in true scientific spirit be- 

 gan to make comparative observations, and in 

 1678 he described and figured spermatozoa of the 

 rabbit and frog among others. 



The credit of this discovery seems to me to be- 

 long rightly to the investigator whose wide experi- 

 ence in the field of microscopical anatomy and 

 whose scientific acumen enabled him to grasp the 

 possible significance of the discovery; not to the 

 chance observer who caUed Leeuwenhoek 's atten- 

 tion anew to the subject. 



5 Phil. Trans., Vol. 21. 



