Onth.eDevelojpmentof^2iQ.tQX\2i{n Organic Infusions. 169 



various forms of these organisms is necessary before the h^^othesis 

 of their spontaneous generation can serve as a safe guide in 

 scientific investigation. 



The experiments recorded below were made ^ith infusion of 

 hay and ^ith infusion of turnip, sometimes with the addition of a 

 few fragments of pounded cheese. It is necessary at once to 

 call attention to three precautions w hich we have taken, and which 

 we think are indispensable: — 1. Recognizing the fact that the 

 presence of lumps is a possible source of error, we excluded these 

 from our infusion, either by filtration or by decantation. 2. To 

 ensure the satisfactory exposure of the whole contents of the tube to 

 the boiling temperature, we, as a rule, completely submerged our 

 experimental tubes in boihng water for a period vanning from 

 five minutes to half an hour. 3. '•The substances used in pre- 

 paring the infusions being necessarily of a very heterogeneous 

 nature, we always examined samples of the infusions before and 

 after boiling, at the time of closing the tubes, and were thus able 

 ^to determine whether any chanr/e had taken place in the visible 

 particles contained in the fluid after a lapse of time. 



The microscopes used by us throughout, working side by side 

 with samples from the same infusion, were a Hartnack's 8tative YIU. 

 objective Xo. 10 a immersion, ocular 4, belonging to the anatomical 

 department of the University Museum, and a large Powell and 

 Lealand belonging to the EadcHife Trustees, which is proAided 

 with a y'-^ and a -gL objectiA-e. The former of the tr^'o English 

 glasses was more usually employed than the latter, on account of 

 its greater convenience in manipulation. 



Api^earances in freshhj i^repared infusions. — Since the objects 

 seen in such infusions are remarkable, and have doubtless some- 

 times led to error in subsequent examination of infusions, we may 

 draw attention to them now. In such freshly prepared infusions 

 we have not unfrequeutly seen appearances agreeing very closely 

 with some of those figured by Dr. Bastian in his book as coming 

 into existence after boiling, sealing, and preservation in a warm 

 chamber. A freshly prepared and boiled strong infusion of hay 

 may present shreds of vegetable fibre, a considerable number of 

 dead Bacterium termo (some two or three to the field), minute, 

 highly refringent spherules, varnng from the size of a blood- 

 corpuscle to the smallest size visible ; and such spherules are 

 often present in pairs, forming figure-of-8-shaped bodies, both 

 smaller and larger than Bacterium and of different optical character. 

 Further, dumb-bell-shaped bodies are not unfrequeutly to be ob- 

 served of similar form and size to Bacteria, but coarser in outline ; 

 they dissolve on addition of IICI, which Bacteria do not*. All 

 these bodies exhibit constant oscillatory (BrowTiian) movements. 

 The addition of new cheese to such an infusion (as shown by 



* In the most carefully guarded of the experiments published by Dr. Child 

 a few years since in the ' Proceedings of the Royal Society,' a very small 

 number of bodies similar to these were obtained ; and we suggest that they were 

 of the same nature. 



