June 6, 1913] 



SCIENCE 



879 



diluted milk and the fewest in that contain- 

 ing the most water. 



IV. When suspended in aqueous mixtures 

 containing from 5 per cent, to 42 per cent, of 

 chemically pure glycerin and held at — 20° C, 

 a very large percentage of B. coli remain alive 

 for at least sis months. 



V. At + 37° C, B. coli in water or in 5 per 

 cent, to 20 per cent, glycerin" die rapidly, 

 few if any remaining alive at the end of 

 72 hours. The death rate diminishes as the 

 holding temperature is lowered, though it is 

 still marked even just ahove 0° C; but at a 

 temperature slightly lower a sudden change 

 appears, the death rate at and below that 

 point being but little, if any, greater than at 

 — 20° C. 



VI. By covering a 24-hour growth on agar 

 with a sterile 10 per cent, cane sugar solution, 

 and holding at — 10° C, stock cultures of B. 

 subtilis, B. aurococcus, B. megaterium, B. 

 fluorescenSj B. proteus and Sarcina aurantia- 

 cus have been kept in a vigorous condition 

 (without transferring) for eight months. 



From these results the following conclu- 

 sions may be drawn: 



Low temperatures alone do not destroy bac- 

 teria. On the contrary, they appear to favor 

 bacterial longevity doubtless by diminishing 

 destructive metabolism. Frozen food mate- 

 rials, such as ice cream, milk and egg sub- 

 stance, favor the existence of bacteria at low 

 temperatures, not because they are foods, but 

 apparently because they furnish physical con- 

 ditions somehow protective of the bacteria. 



It seems likely that water-bearing food ma- 

 terials as well as sugar solutions, glycerin so- 

 lutions, etc., freeze in such a way that most of 

 the bacteria present are extruded from the 

 water crystals with other non-aqueous matters 

 (including air) and lie in or among these 

 matters without being crushed or otherwise 

 injured; while in more purely watery suspen- 



^ Glycerine mixtures much exceeding 20 per cent., 

 at temperatures above the freezing point of water, 

 act as mild antiseptics. Under 20 per cent, this 

 is not the case, the death of the bacteria appar- 

 ently resulting from lack of food, as it does not 

 occur when a small amount of peptone is present. 



sions, and, above all, in water itself in which 

 the whole mass becomes solidly crystalline, 

 they have no similar refuge but are perhaps 

 caught and ultimately mechanically destroyed 

 between the growing crystals. This theory 

 wovild explain the absence of live bacteria in 

 clear ice, their comparative abundance in 

 " snow " ice and " bubbly " ice, and also the 

 fact that the more watery food materials when 

 frozen contain the fewest, and the least watery 

 the most, living bacteria. 



The comparatively rapid death of bacteria 

 in non-nutrient materials at higher tempera- 

 tures and their slower dying at lower tem- 

 peratures agi-ees well with the theory of 

 simple starvation or destructive metabolism. 

 At the higher temperatures they perish 

 quickly because they burn themselves out 

 quickly ; at the lower, more slowly, because they 

 consume themselves more slowly. At tempera- 

 tures where metabolism ceases altogether they 

 continue to exist in a state of suspended vital- 

 ity similar to that exhibited by many other 

 and higher plants which in the far north are 

 subjected without apparent injury for long 

 periods to temperatures much below the 

 freezing point of water. 



S. C. Keith, Jr. 



Massachusetts Institute of Technology. 



HEMOPHOEIC FUNCTION OF THE THORACIC DUCT 

 IN THE CHICK 



In a recent investigation of the develop- 

 ment of the thoracic duct in the common fowl, 

 the writer studied also certain aggregations of 

 mesodermal cells correlated with the develop- 

 ing duct, and considered by Sala,' more than 

 ten years ago, as " cords " of mesenchymal 

 cells out of which were " hollowed " the rudi- 

 ments of the duct. 



The writer believes, and in the near future 

 will publish evidence to substantiate the be- 

 lief, that these aggregations of mesodermal 

 (mesenchymal) cells comprise developing blood 

 cells which are differentiated in situ out of 

 the indifferent mesenchymal syncytium, that 

 these blood cells then gain access to the Ijrmph 



^ Sala, Bieherche fatta nel Lab. di Anat, Norm, 

 della E. Unw. di Boma, Vol. 7, 1900. 



