446 NOTES. 



could prove such a difference in the degree of oxygenation of the blood 

 in different portions of the insect, we must speak physiologically of 

 arteries and veins. Now this, it would seem, is sometimes the case, as 

 in the external breathing organs of many insect-larvae living in the 

 water, or in the very curious conical structures at the termination of 

 the intestine of flies, which, on account of their extraordinary develop- 

 ment of tracheae, there is now a very general disposition to regard as in- 

 testinal branchiae. In this last instance certainly it is not very clear 

 how they are to act as organs of respiration, since it is certain that 

 flies do not carry oxygenated water in the end of the intestine, and no 

 observations as to the inhalation of air through it have been made to 

 my knowledge. However, a small difference in the oxygenation of the 

 fluids must, no doubt, exist in different portions of the body even in 

 insects. 



Note SI, page 181. 1 will" here briefly describe an observation acci- 

 dentally made, but frequently repeated, which suggests the idea that 

 some animals, and especially Infusoria, may possibly be capable of 

 absorbing (and even assimilating ?) carbonic acid. In infusions pre- 

 pared with the water procurable at Wiirzburg, which contains a great 

 deal of lime, an excessively thin film is rapidly formed of carbonate of 

 lime, beneath which various Infusoria crowd in masses. If the water 

 is slightly shaken, the fragments of this film roll up into little cylinders, 

 thus enclosing a minute quantity of air, as may be seen by examination 

 with a microscope ; since these can be obtained only from the surface of 

 the water, they must certainly be rich in carbonic acid. If now we trans- 

 fer these little tubes containing air with some infusoria to a moist 

 chamber, we see th^t they are not unfrequently consumed by the infu- 

 soria, and if we then watch for some length of time one of the specimens 

 which has just fed, we shall soon detect that the air in the lime-tubes 

 disappears, and finally the tubes and the air contained in them are com- 

 pletely absorbed. I have frequently repeated this observation, and 

 have particularly noted whether or no the air might not escape in the 

 form of minute bubbles from the oral opening or be removed in the 

 pellets of food ; but this was never the case, and I can most positively 

 assert that all the air was perfectly absorbed. Of course this is not 

 hereby proved ; still, though I was not able to carry the observation 

 any further, I regard it as sufficiently interesting to be recorded here. 

 Bert says very decidedly in one of his papers read at the Sorb<>nne, ' On 

 the Influence of Light on Living Beings : ' 'On the other hand, infusoria 

 containing green matter decompose carbonic acid in the same way as 

 vegetable cells.' On what ground of exact experiment this bold asser- 

 tion is made I do not know. 



Note 82, page 181. Only an incidental reference is made in the text 

 to those other gaseous constituents of the atmosphere which, like car- 

 bonic acid, are endurable in small proportions, but extremely injurious 



