Nothing can symbolise the contents of this life-saving apparatus (6,4)
I believe the answer is:
oxygen mask
'this life-saving apparatus' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'nothing can symbolise the contents' is the wordplay.
I cannot quite see how this works, but
'nothing' could be 'o' (looks like zero - 0) and 'o' is found in the answer.
'contents' could be 'mas' (MA is an example) and 'mas' is located in the answer.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Another definition for oxygen mask that I've seen is " Breathing aid".)