182 
Notes. 
Since the time of Schonbein it has been known that blood, or more 
particularly haemoglobin, has the property of causing guaiacum to turn 
blue in the presence of hydrogen peroxide. On the strength of their 
similarity in this respect, Raciborski goes so far as to state that 
* leptomin performs, in vascular plants, a function analogous to that of 
haemoglobin in the higher, and haemocyanin in the lower, animals, in 
that it is a vehicle charged with oxygen maintaining internal respiration, 
that is, a supply of oxygen from the phloem and the laticiferous system 
to the adjacent tissues/ 
Now it is well known that haemoglobin possesses in a high degree 
the property of combining with free oxygen and of readily parting with 
it : but it is not clear that this property is expressed by, or indeed 
stands in any relation with, its power of decomposing hydrogen peroxide. 
For many tissues of the animal body, as also freshly prepared blood- 
fibrin, have been found to decompose hydrogen peroxide, without 
there being any suggestion that they are, like haemoglobin, of physio- 
logical importance as oxygen-carriers. This is precisely the position 
of the matter as regards leptomin. Because it decomposes hydrogen 
peroxide, it does not follow that it is an oxygen-carrier like haemo- 
globin ; there is no evidence whatever to show that it shares in any 
degree the property of combining with oxygen which is so characteristic 
of haemoglobin. Nor is there any ground for distinguishing physio- 
logically, as Raciborski apparently does, between the ‘ leptomin ’ of 
the phloem and the laticiferous tissue, and the ‘ leptomin ’ of coco-nut 
milk or of potato pulp. 
The analogy which Raciborski seeks to establish between * leptomin ’ 
and haemoglobin, attractive as it is, would seem to be premature, to 
say the least. The fact that there exist, in the body of both animals 
and plants, substances which can decompose hydrogen peroxide, still 
awaits, I believe, its physiological interpretation; and its significance 
is rendered all the more problematical by the great improbability of 
the occurrence of hydrogen peroxide in the living organism. It is, 
however, possible to conceive that unstable, highly oxidized, organic 
substances may be formed and distributed within the organism, and 
that their loosely combined oxygen can only be made available in the 
tissues on decomposition by the substances which we now only know 
by their action on hydrogen peroxide ; it is not inconceivable, for 
instance, that the decomposition of oxy-haemoglobin may be effected 
in this way. 
