Respiration of Plants and Animals. 23 



indeed being made the basis of a valuable test for blood, 

 with which the name of Dr. Day, of Geelong, is associated. 

 Tincture of guaiacum and peroxide of hydrogen may be 

 brought together without any change of colour appearing ; 

 but as soon as a minute trace of blood or haemoglobin is 

 added a deep blue is struck. The presence of ozone in the 

 blood, as first asserted by Professor Alexander Schmidt in 

 1862, and confirmed by W. Klihne (Lehrhuch der Physiolo- 

 gischen Cheinie, 1868, p. 214) and others, has been doubted 

 by some physiologists, and indeed quite lately by Dr. Michael 

 Foster in his Textbook of Physiology, first edition, 1877, 

 p. 240. As there is not yet by any means unanimity of 

 opinion as to the nature of ozone and its characteristic re- 

 actions, the dispute may be mainly about names, there being 

 really agreement that the oxygen in the blood is more 

 active, i.e., combines more readily with reducing substances, 

 than the ordinary form existing in the atmosphere. The 

 transformations undergone by oxygen in the vegetable 

 economy do not seem to have been traced in the same way. 

 For the purpose of discovering the present state of know- 

 ledge on the subject I have gone through the most likely 

 sections in Sachs' Textbook of Botamy, in Watts' Dictionary 

 of Chemistry, including the supplements, and in the Dic- 

 tionnaire de Chemie, of Wurtz, as well as through the 

 articles most likely to touch on the subject in the Journal 

 of the Chemical Society, and the Chemisches Gentralblatt for 

 the last few years, and have been able to find nothing but the 

 vaguest statements. My own observations were first made 

 some years ago in the course of a series of experiments 

 mainly designed to test the reliability of the guaiacum test 

 for blood, the results being embodied in a paper in the Aus- 

 tralian Medical Journal for October, 1869. At that time 

 I did not see the full bearing of these observations on the 

 subject now under discussion ; but having occasion again to 

 take the matter up recently I have been able to reach more 

 definite conclusions. The recent experiments have been 

 made chiefly with fruits of different sorts, especially apples 

 and pears, though what is true of them holds good of most 

 other fresh vegetable structures and expressed juices. If a 

 drop of tincture of guaiacum be allowed to fall on a freshly 

 cut surface of an apple or pear, which has not been too 

 long pulled and is not decayed, it will generally be 

 found that a blue colour is quickly struck. Again, if a few 

 crumbs of biscuit or other cooked starch are sprinkled on 



