1 64 NATURAL SCIENCE. Sept.. 



embryology that would contain any substantial addition to Vejdovsky's 

 memoir. The last 500 pages are systematic. 



It is interesting to notice, in reference to our last note,'that Mr. 

 Beddard takes a different view of the relation of the genital ducts to 

 the nephridia from that of Mr. Goodrich. At one time he held that 

 there was evidence for the derivation of a paired nephridial system, 

 like that in Lnmhricns, from a diffuse system, like that in Megaloscokx : 

 later investigations by Spencer, Benham, himself, and especially by 

 Vejdovsky, led him to believe that both diffuse and paired systems 

 are equally ancient. Similarly, at one period of his investigations, he 

 was inclined to abandon, as Mr. Goodrich does in his paper, the 

 current view that the genital ducts were derived from nephridia. 

 Latterly, however, he has returned to the generally-accepted view, 

 and holds that the genital ducts certainly are modified nephridia. 

 He thinks that the difficulty as to the coincidence of generative ducts 

 and nephridia in a segment is cleared up by his discovery of multiple 

 nephridial pores in Octoch^tus and other genera. Moreover, actually 

 in the case of Octochatus midtiporns, he was able to trace the develop- 

 ment of the genital ducts from separated portions of the pronephridia. 



Carbonic Oxide Poisoning. 



In a recent number of the Journal of Physiology (July, 1895) Dr. 

 John Haldane gives the results of experiments he has been making on 

 the process of carbonic oxide poisoning. The experiments were 

 made in connection with his investigation, now in process, into the 

 nature and action of the poisonous gases in the air of coal mines. 

 He concludes that the poisonous action of carbonic acid diminishes as 

 the oxygen tension increases, and vice versa. With an oxygen tension 

 of two atmospheres the poisonous action was abolished in the case of 

 mice. The disappearance of this poisonous action is due to the fact 

 that at high oxygen tensions the animals can dispense entirely with 

 the oxygen-carrying function of haemoglobin. The poisonous action 

 of carbonic acid is entirely due to its power of combining with the 

 haemoglobin of the red corpuscles, and so putting them out of action 

 as oxygen-carriers. 



This adds another to the remarkable series of results Dr. Haldane 

 has obtained. He has already shown that carbonic acid and the 

 organic substances in foul air are not the direct poisons they have 

 been supposed, but that it is the diminution of oxygen-tension, usually 

 associated with their presence, that does the damage. Carbonic oxide 

 has been regarded still more as a direct poison, and the discovery that 

 an increase of oxygen restrains and finally overcomes the disastrous 

 results of its presence has an important practical as well as 

 theoretical bearing. The generation of oxygen, rather than attempts 

 at ventilation, would seem to be the new method for protecting 

 dangerous mines. 



