ON THE ORIGIN OF LIFE. 



213 



dispute ; but in 1683 and subsequent years, Leeuwenhoek* 

 described minute organisms, which we now recognize as bacteria, 

 the origin of which soon became a matter of keen contention. 

 He says : I saw with very great astonishment, especially in 

 the material mentioned " (from the teeth of an old man who 

 had never used a tooth brush) " that there were many extremely 

 small animals which moved about in a most amusing fashion; 

 the largest of these" (represented by him in an admirable 

 figure) " showed the liveliest and most active motion, moving 

 through rain-water or saliva like a fish of prey darts through 

 the water : this form, though few in actual numbers, was met 

 with everywhere. A second form moved round, often in a 

 circle, or in a kind of curve ; these were present in greater 

 numbers. The form of a third kind, I could not distinguish 

 clearly ; sometimes it appeared oblong, sometimes quite round. 

 They were very tiny, in addition to which they moved forward 

 so rapidly that they tore through one another ; they presented 

 an appearance like a swarm of midges and flies buzzing in and 

 out between one another. I had the impression that I saw 

 several thousands in a single drop of water or saliva which was 

 mixed with a small part of the above-named material not 

 larger than a grain of sand, even when nine parts of water or 

 saliva were added to one part of the material taken from the 

 incisor or molar teeth. Further examination of the material 

 showed that out of a large number which were very different 

 in length, all were of the same thickness. Some were curved, 

 some straight, lying irregularly and interlaced." Since, he says, 

 " I had seen minute living animalculse of the same shape in 

 water, I endeavoured most carefully to observe whether these 

 also were living or not, but I was unable to recognize even 

 the slightest movement as a sign of life." Erasmus Darwin,-|- 

 speaking of these organisms in 1794, says, perhaps they may be 

 creatures of stagnation or putridity or perhaps no creatures at 

 all Leeuwenhoek's demonstration of the presence of minute 

 organisms in various kinds of putrefying organic matter and 

 even in rainwater was to others an occasion for again calling in 

 spontaneous generation as affording an explanation of the 

 presence of these simple living forms. But he stuck to his views 

 of their function, and to his opposition to the theory of spontaneous 

 generation, which had to wait almost until our time before it was 



* Omnia Opera, seu Arcana Naturae ope microscopiorum exactissimorum 

 detecta, Lugd. Bat., 1722. 



t Zoonomia ; or the Laws of Organic Life, London, 1794-1798. 



